1. Field of the Invention
The present invention relates to a combined detector having a plurality of sensors for respectively detecting different danger-identifying signals in a fire alarm system or the like.
2. Description of the Prior Art
Various conventional sensors are known to monitor environmental changes. For example, an ionization type smoke detector, a photoelectric smoke detector, a heat detector, and a flame detector have been used in a fire alarm system; a gas leakage detector or the like, in a gas leakage alarm system; and an ultrasonic detector or the like, in a burglar alarm system. Conventionally, these detectors generate outputs only when detection outputs are required. However, a so-called analog detector has recently been used to improve reliability of the system as a whole. This system constantly monitors a detection output so as to compensate for a failure of the detector and deterioration over time.
Various systems are also known which obtain installation position signals of individual detectors at a central monitoring unit so as to obtain more precise information. With the recent development of microcomputers, specific addresses are assigned to individual detectors so as to obtain detection outputs of the respective detectors by a sampling system through a common transmission line from a central monitoring unit. Japanese Utility Model Disclosure No. 59-178794 (Nov. 29, 1984) describes an analog detector using sampling system including both of the above techniques as shown in FIG. 2 herein. More specifically, a transmission circuit TM in a detector to converts an address signal which is supplied from a central monitoring system through a transmission line l by a sampling system into a format compatible with an address comparator AC. The address comparator AC detects whether an accessed address coinciding with an address set by an address setter AS is present. The address comparator AC supplies an address coincidence signal as an output when the addresses coincide with each other. The address coincide signal is supplied to an analog/digital converter AD and a switching transistor Tr and drives those elements. When the switching transistor Tr is driven, an ionization smoke detector I is operated and a voltage signal corresponding to the concentration of smoke present in an external ion chamber Io is generated. The voltage signal is supplied to the A/D converter AD and converted into a digital signal and then supplied to the transmission line l through the transmission circuit TM. At the central monitoring unit, necessary information of designated detectors can be obtained by the address supplied in advance and the signal received in response to the address through the transmission line l.
A problem exists when a transmission system of an analog detector in the sampling system described above is used without modification to a combined detector having a plurality of sensors in a single sensor device. In order to obtain information of all sensors in a combined detector connected to a transmission line, the information transmission time per sensor and the sampling cycle are prolonged. Therefore, the access interval of each detector is prolonged and quick information acquisition as a main object of the monitoring system cannot be achieved.